The safe is in a garage in the mid Atlantic. Garage is not heated nor cooled.

Any devices come to mind in which stability, at least in a relative sense, can be maintained?

Powered by electricity not a good option as no holes are drilled in the safe for an electrical cord, nor do I wish to permanently ruin this fine antique safe.

While I'm at it, any way to date my safe? Obviously no earlier than 1906 as it was patented 03 April 1906, Hall's.